Liquid phase adsorption of volatile Organo Sulphur compounds in presence of a Cationic surfactant : Process innovations towards dearomatization of sewage waste water

Abstract

Odorous emissions from sewers and sewage wastewater treatment plants are a complex mixture of volatile organic compounds that can cause a nuisance to adjacent populations and contribute significantly to atmospheric pollution. Odour abatement and control is thus a major issue for Sewage Treatment Plants. A quantitative Odour Assessment and Control Scheme (OACS) describing various methods for the assessment and control of odour have been developed. Assessment of odour intensity is carried out by panel based olfactometry method, with the help of trained human sniffers. Psychophysical laws are applied and validated to evaluate odour concentration in the semi solid, liquid and gas phases. For raw sewage, Beidler’s equation represents the intensity-concentration relationship best. Odours from waste water treatment plant have been traditionally treated using physicochemical processes, such as scrubbing, adsorption, condensation and oxidation, Adsorption is the most effective technique to control the odour of raw sewage. Granular Activated Carbon (GAC) is a common adsorbent material for the adsorption of Volatile Organo-Sulphur Compounds (VOSCs). Waste water contains so many cationic surfactants, coming from household cleaners, soap, shampoo, saving cream etc. In presence of cationic surfactants removal of VOSCs decreases with GAC. Adsorption capacity of GAC was enhanced by functionalization with different alkaline solutions such as NaOH , KOH, NH3 etc. The alkali Functionalized Activated Carbons (FACs) have higher surface area and pore volume, and reduction of oxygen containing functional groups than precursor GAC. Analytical methods characterize odours in terms of their chemical composition and attempt to quantify the odorants present by Gas Chromatography Mass Spectrometer (GC-MS) equipped with Pulse Flame Photometric (PFPD) Detector The time variant odour concentration profile (Olfactometry based) goes at per with the time variant VOSCs concentration (GCMS outputs) for all the four components like Methyl Mercaptan (CH3SH), Ethyl Mercaptan (C2H5SH), Dimethyl di-sulphide (CH3SCH3) and Carbon di-sulphide (CS2), having low enough odour threshold values. Successful field use of physical adsorption using GAC and different FACs will require measurements which would account for the extreme variations in sewage composition, sewage age, sewage conditions and type of secondary treatment provided. It is important to determine the magnitude and distribution of such variability and the impact on emission of the VOCs in order to design an accurate emission monitoring and control programme. VOSCs undergo physical and chemical adsorption through film and pore-diffusion. They form surface complexes with the functional groups of GAC and FACs sample. An increase in the adsorption capacity of FACs is primarily due to chemisorption, ensured by the ‘good-fits’ in the pseudo kinetics and Boyd’s film diffusion models.